Elenco 130-in-1 Electronics Playground - Manual (Page 128)

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Wouldn’t you like to make a kitchen timer that you can
use for cooking meals? This circuit gives out a buzzer
sound for 1 to 2 seconds and automatically stops.
Slide the switch to position B, build the circuit, and set
the switch to position A to turn it on. Set the control
to position 2 on the dial, and press the key to start the
timer. After about 40 seconds, the timer sounds for 1
to 2 seconds and stops. Use the graph you made in
project 107 to preset this timer.
Look at the schematic. When the preset time is up,
the comparator (IC 2) sends out an output. After a
time lag of 1 to 2 seconds produced by R and C, the
transistor Q1 turns on to stop the multivibrator. The
silicon diode discharges C and restores the circuit to
the original state when the timer is restarted.
Notes:
EXPERIMENT #108: COOKING TIMER
Wiring Sequence:
1-29
2-30
3-114
5-83-70-104-116-118-137-48-26-121
27-68
93-63-28-131
46-85
91-103-65-47
92-88-64-113
81-84-87-66
67-82-89
69-94-117-138-129
86-90-115-130
119-124
122-132
Schematic